Voice Port
Site D Router Version Information
Cisco Internetwork Operating System Software IOS (tm) C2600 Software (C2600-IS-M), Version 12.0(2)XC2, EARLY Copyright (c) 1986-1999 by cisco Systems, Inc. Compiled Wed 20-Jan-99 19 39 by rnapier Image text-base 0x80008088, data-base 0x8096A6F4 ROM System Bootstrap, Version 11.3(2)XA3, PLATFORM SPECIFIC RELEASE SOFTWARE (fc1) ROM C2600 Software (C2600-IS-M), Version 12.0(2)XC2, EARLY DEPLOYMENT RELEASE SOFTWARE (fc1) SiteD2610 uptime is 16 hours, 14 minutes System restarted by power-on System...
Hunt Groups
It's often convenient to bundle multiple phone lines using a single phone number. While each line has a unique phone number, external users can dial a single number and the system will automatically connect them to the first available phone line. This concept offers the following benefits. A single number is easier for users to remember Users do not have to manually try each phone line until they find an available line It allows administrators to take individual lines in and out service without...
Enable Logging and Syslog
The router generates informational messages as events occur. This information can be critical when attempting to resolve network issues. Messages can be stored in the router's internal memory log as well as on an external syslog server. Cisco also provides control over the severity of messages that are transmitted, allowing managers to filter out unnecessary information. The steps for enabling internal and external logging follow. logging buffered log-size info-level where buffered indicates...
VoIP Dial Peers
The next step is to enable calls between VoIP devices. VoIP dial peers perform this task by associating a phone number (destination-pattern) with a remote IP address. In addition to this task, VoIP dial peers provide an ability to specify the type of QoS associated with the call. The ability to specify QoS on a per-call basis allows administrators to vary the type of QoS employed based upon destination address and or traffic path. This provides a method for offering differentiated service...
Traffic Shaping
With IOS v11.2, Cisco introduced generic traffic shaping to help control the rate of traffic flow through the router. Generic traffic uses a basic token-bucket mechanism to limit the output rate of traffic. Generic traffic shaping operates at the interface descriptor block (IDB) level within the software, making it applicable to both physical and logical interfaces. This means that it can be used on subinterfaces, as well as physical interfaces.
Comparing the Voice Encoding Techniques
Voice quality is a subjective measurement. Different people react differently to each compression technique. To help quantify the quality of a given technique, the mean opinion score (MOS) scale was developed. To develop the MOS numbers, test listeners rated various speech patterns sent through each compression technique for quality of sound on a scale of 1 to 5, with 5 being the best. The results are then averaged to produce the mean opinion score. Table 3-5 includes the various compression...
Compressed Real Time Transfer Protocol
One of the simplest techniques for reducing delay is to simply send less data. The basic principle is that less data require less time to send. Voice over IP traffic uses the Real-Time Transport Protocol (RTP) as defined by RFC 1890. RTP is a session-layer protocol which rides on top of UDP and provides hooks for real-time streaming applications such as voice and video. The RTP header is 8 bytes and when combined with an 8-byte UDP header and a 20-byte IP header, RTP traffic consumes 40 bytes...
FXS and FXO Interfaces
As mentioned earlier, FXS interfaces must provide line voltage, ring generation, off-hook detection, call-progress indicators (ring-back, busy sig- Block diagram of Cisco 3640 router with an NM-2v and two VIC-2FXS. Block diagram of Cisco 3640 router with an NM-2v and two VIC-2FXS. interface Ethernet1 0 no ip address shutdown interface Ethernet1 1 no ip address shutdown interface Serial1 0 no ip address shutdown interface Serial1 1 no ip address shutdown Figure 6-2 Voice port configuration...
Signaling Techniques
E&M signaling is not restricted to the 2-wire implementations discussed with FXO and FXS configurations. The 2- and 4-wire implementations describe the number of wires used to transmit the audio signals to and from the telephony devices. The 2-wire implementation is similar to a standard phone in that full-duplex audio signals are transmit- E&M Signaling Pinout and Descriptions E ear or earth M mouth or magnet SB signal battery Signal from trunking side to signaling I, II, III, IV, Signal from...
IP Precedence with Voice Traffic
Since a voice-enabled router is the source station for voice over IP traffic, Cisco included a simple mechanism for setting the IP precedence bit for VoIP traffic originating from the router. To accomplish this, Cisco added the command ip precedence to the VoIP dial-peer configuration. This allows the precedence bit and, therefore, the network class of service to be set on an individual VoIP session basis. Here is the syntax for the dial-peer command where n is a number from 0 to 5 representing...
Challenges for Frame Relay
Frame-relay networks introduce many design and implementation challenges for transporting VoIP traffic. These challenges and their resolutions are listed below. 2. Preventing nonvoice traffic from delaying voice traffic 3. Minimizing delay and delay variance without effecting other network-layer protocols 4. Enabling QoS functions without degrading performance on the frame-relay connected routers 5. Enabling QoS functions without affecting the traffic over other PVCs 6. Identifying all routers...