Link Layer
OSI Protocols Session Layer
The session-layer implementation of the OSI protocol suite consists of a session protocol and a session service. The session protocol allows session-service users (SS-users) to communicate with the session service. An SS-user is an entity that requests the services of the session layer. Such requests are made at Session-Service Access Points (SSAPs), and SS-users are uniquely identified by using an SSAP address. Figure 32-4 shows the relationship between the SS-user, the SSAP, the session...
Ethernet and IEEE 8023 Frame Formats
Figure 7-4 illustrates the frame fields associated with both Ethernet and IEEE 802.3 frames. Figure 7-4 Various frame fields exist for both Ethernet and IEEE 802.3. 50F Slart'-T'l 'Frarnfl Drill Till pr 50F Slart'-T'l 'Frarnfl Drill Till pr The Ethernet and IEEE 802.3 frame fields illustrated in Figure 7-4 are as follows. Preamble The alternating pattern of ones and zeros tells receiving stations that a frame is coming (Ethernet or IEEE 802.3). The Ethernet frame includes an additional byte...
Circuit Switching
Circuit switching is a WAN switching method in which a dedicated physical circuit is established, maintained, and terminated through a carrier network for each communication session. Circuit switching accommodates two types of transmissions datagram transmissions and data-stream transmissions. Used extensively in telephone company networks, circuit switching operates much like a normal telephone call. Integrated Services Digital Network (ISDN) is an example of a circuit-switched WAN technology,...
RSVP Reservation Style
Reservation style refers to a set of control options that specify a number of supported parameters. RSVP supports two major classes of reservation distinct reservations and shared reservations. Distinct reservations install a flow for each relevant sender in each session. A shared reservation is used by a set of senders that are known not to interfere with each other. Figure 43-2 illustrates distinct and shared RSVP reservation-style types in the context of their scope. Each supported...
Basic QoS Architecture
The basic architecture introduces the three fundamental pieces for QoS implementation (see Figure 46-1) QoS within a single network element (for example, queuing, scheduling, and traffic shaping tools) QoS signaling techniques for coordinating QoS from end to end between network elements QoS policy, management, and accounting functions to control and administer end-to-end traffic Figure 46-1 A basic QoS implementation has three main components. Figure 46-1 A basic QoS implementation has three...
OSI Connection Oriented Network Service
OSI connection-oriented network service is implemented by using the Connection-Oriented Network Protocol (CONP) and Connection-Mode Network Service (CMNS). CONP is an OSI network-layer protocol that carries upper-layer data and error indications over connection-oriented links. CONP is based on the X.25 Packet-Layer Protocol (PLP) and is described in the ISO 8208 standard, X.25 Packet-Layer Protocol for DTE. CONP provides the interface between CMNS and upper layers. It is a network-layer service...
Security Issues When Connecting to the Internet
When you connect your private network to the Internet, you are physically connecting your network to more than 50,000 unknown networks and all their users. Although such connections open the door to many useful applications and provide great opportunities for information sharing, most private networks contain some information that should not be shared with outside users on the Internet. In addition, not all Internet users are involved in lawful activities. These two statements foreshadow the...
Packet Layer Protocol PLP
PLP is the X.25 network-layer protocol. PLP manages packet exchanges between DTE devices across virtual circuits. PLPs also can run over Logical-Link Control 2 (LLC2) implementations on LANs and over Integrated Services Digital Network (ISDN) interfaces running Link Access Procedure on the D channel (LAPD). The PLP operates in five distinct modes call setup, data transfer, idle, call clearing, and restarting. Call setup mode is used to establish SVCs between DTE devices. A PLP uses the X.121...
Apple Talk Update Based Routing Protocol AURP
The AppleTalk Update-Based Routing Protocol (AURP) is a transport-layer protocol in the AppleTalk protocol suite that allows two or more AppleTalk internetworks to be interconnected through a Transmission-Control Protocol Internet Protocol (TCP IP) network to form an AppleTalk WAN. AURP encapsulates packets in User-Datagram Protocol (UDP) headers, allowing them to be transported transparently through a TCP IP network. An AURP implementation has two components exterior routers and AURP tunnels....
DECnet Phase IV Digital Network Architecture DNA
The Digital Network Architecture (DNA) is a comprehensive layered network architecture that supports a large set of proprietary and standard protocols. The Phase IV DNA is similar to the architecture outlined by the OSI reference model. As with the OSI reference model, the Phase IV DNA utilizes a layered approach, whereby specific layer functions provide services to protocol layers above it and depend on protocol layers below it.
Establishing a Security Perimeter
When you define a network security policy, you must define procedures to safeguard your network and its contents and users against loss and damage. From this perspective, a network security policy plays a role in enforcing the overall security policy defined by an organization. A critical part of an overall security solution is a network firewall, which monitors traffic crossing network perimeters and imposes restrictions according to security policy. Perimeter routers are found at any network...
Apple Talk Transaction Protocol ATP
The AppleTalk Transaction Protocol (ATP) is a transport-layer protocol in the AppleTalk protocol suite that handles transactions between two AppleTalk sockets. A transaction consists of transaction requests and transaction responses, which are exchanged by the involved socket clients. The requesting socket client sends a transaction request asking that the receiving client perform some action. Upon receiving the request, the client performs the requested action and returns the appropriate...
ADSL Standards and Associations
The American National Standards Institute (ANSI) Working Group T1E1.4 recently approved an ADSL standard at rates up to 6.1 Mbps (ANSI Standard T1.413). The European Technical Standards Institute (ETSI) contributed an annex to T1.413 to reflect European requirements. T1.413 currently embodies a single terminal interface at the premises end. Issue II, now under study by T1E1.4, will expand the standard to include a multiplexed interface at the premises end, protocols for configuration and...
Asymmetric Digital Subscriber Line ADSL
It allows more bandwidth downstream---from an NSP's central office to the customer site---than upstream from the subscriber to the central office. This asymmetry, combined with always-on access (which eliminates call setup), makes ADSL ideal for Internet intranet surfing, video-on-demand, and remote LAN access. Users of these applications typically download much more information than they send. ADSL transmits more than 6 Mbps to a subscriber, and as much as 640...
ATM Cell Header Format
An ATM cell header can be one of two formats UNI or the NNI. The UNI header is used for communication between ATM endpoints and ATM switches in private ATM networks. The NNI header is used for communication between ATM switches. Figure 20-4 depicts the basic ATM cell format, the ATM UNI cell-header format, and the ATM NNI cell-header format. Figure 20-5 An ATM cell, UNI cell, and ATM NNI cell header each contain 48 bytes of payload. Figure 20-5 An ATM cell, UNI cell, and ATM NNI cell header...
Figure 718 The Gigabit Ethernet draft specifies these distance specifications for Gigabit Ethernet
NB Ghsiances ivu 'Ml'I caryijiy may change in nal Ep 1icatipn. i The physical media attachment (PMA) sublayer for Gigabit Ethernet is identical to the PMA for Fibre Channel. The serializer deserializer is responsible for supporting multiple encoding schemes and allowing presentation of those encoding schemes to the upper layers. Data entering the PHY will enter through the PMD and will need to support the encoding scheme appropriate to that medium. The encoding scheme for Fibre Channel is 8B...
LAPB Frame Format
LAPB frames include a header, encapsulated data, and a trailer. Figure 17-6 illustrates the format of the LAPB frame and its relationship to the PLP packet and the X.21bis frame. The following descriptions summarize the fields illustrated in Figure 17-6 F ag Delimits the beginning the end of the LAPB frame. Bit stuffing is used to ensure that the flag pattern does not occur within the body of the frame. Address Indicates whether the frame carries a command or a response. Control Qualifies...
Figure 308 Subnet mask bits come from the highorder bits of the host field
Various types of subnet masks exist for Class B and C subnets. The default subnet mask for a Class B address that has no subnetting is 255.255.0.0, while the subnet mask for a Class B address 171.16.0.0 that specifies eight bits of subnetting is 255.255.255.0. The reason for this is that eight bits of subnetting or 28 - 2 (1 for the network address and 1 for the broadcast address) 254 subnets possible, with 28 - 2 254 hosts per subnet. The subnet mask for a Class C address 192.168.2.0 that...
RSVP Messages
RSVP supports four basic message types reservation-request messages, path messages, error and confirmation messages, and teardown messages. Each of these is described briefly in the sections that follow. A reservation-request message is sent by each receiver host toward the senders. This message follows in reverse the routes that the data packets use, all the way to the sender hosts. A reservation-request message must be delivered to the sender hosts so that the hosts can set up appropriate...
SNMP Reference SNMPv1 Message Formats
SNMPv1 messages contain two parts a message header and a protocol data unit. Figure 52-4 illustrates the basic format of an SNMPv1 message. Figure 52-4 An SNVPv1 message consists of a header and a PDU. Simple Network Management Protocol (SNMP) SNMPv1 message headers contain two fields Version Number and Community Name. The following descriptions summarize these fields Version Number Specifies the version of SNMP used. Community Name Defines an access environment for a group of NMSs. NMSs within...
SMRP Multicast Transport Services
SMRP is designed to enable routers and end stations to exchange multicast packets over network-layer protocols. SMRP provides the capability to manage multicast address assignment and enables a single source to send data addressed to a unique multicast group address. Receivers join this group if they are interested in receiving data for this group. In support of these functions, SMRP involves a number of services. The discussions that follow focus on the key processes and technologies that...
Searching Documents
You can search the current document for a word or phrase, or you can search multiple documents. Use the Find command to search a document for a specific word or phrase, as follows 1. Select Find from the Edit menu. 2. Enter the text you want to find in the Text to Find field. To find text with specific capitalization, check the Match Case box. To start searching from the beginning of the document, check the Start From Top box. 3. Click on the Find button. If the text is found, it is...
ATM Reference Model
The ATM architecture uses a logical model to describe the functionality it supports. ATM functionality corresponds to the physical layer and part of the data link layer of the OSI reference model. The ATM reference model is composed of the following planes, which span all layers Control This plane is responsible for generating and managing signaling requests. User This plane is responsible for managing the transfer of data. Management--- This plane contains two components o Layer management...
Figure 373 An APPN routing CoS table can include special character returns and route weighting information
IBM System Network Architecture (SNA) Routing APPN routing CoS table entries include CoS name, index, APPN Transmission Priority (TPRI), characteristics, and APPN CoS Weighted Field (WF). The CoS name is a standard name, such as SEC3, that is agreed upon by conventions. The index field entry enables computed weight values for route components to be stored and retrieved. This entry points to the entry in the CoS weight array where the weights for the CoS are stored. APPN TPRI identifies the...
Ibm Sna Data Link Control
The SNA data-link control (DLC) layer supports a number of media, each of which is designed to provide access to devices and users with differing requirements. SNA-supported media types include mainframe channels, SDLC, X.25, and Token Ring, among other media. A standard SNA mainframe channel attachment provides a parallel-data channel that uses direct memory access (DMA) data-movement techniques. A mainframe channel connects IBM hosts to each other and to communications controllers via...
VINES Internetwork Protocol VIP
VINES network-layer addresses are 48-bit entities subdivided into network (32 bits) and subnetwork (16 bits) portions. The network number is better described as a server number because it is derived directly from the server's key (a hardware module that identifies a unique number and the software options for that server). The subnetwork portion of a VINES address is better described as a host number because it is used to identify hosts on VINES networks. Figure 33-2 illustrates the VINES...
ADSL Technology
ADSL depends on advanced digital signal processing and creative algorithms to squeeze so much information through twisted-pair telephone lines. In addition, many advances have been required in transformers, analog filters, and analog digital (A D) converters. Long telephone lines may attenuate signals at 1 MHz (the outer edge of the band used by ADSL) by as much as 90 dB, forcing analog sections of ADSL modems to work very hard to realize large dynamic ranges, separate channels, and maintain...
NLSP Hierarchical Routing
NLSP supports hierarchal routing with area, domain, and global internetwork components. An area is a collection of connected networks that all have the same area address. A domain is a collection of areas that belong to the same organization. A global internetwork is a collection of domains that usually belong to different organizations but with an arms-length relationship. Areas can be linked to create routing domains, and domains can be linked to create a global internetwork. NLSP supports...