Vgateway Config
Using Policy Maps
After you have identified the interesting traffic, you can mark it or set policies for it. Marking traffic involves setting the DSCP bits or the CoS bits. You should classify and mark traffic as close to the end devices as possible, because classifying traffic uses router and switch resources. This is most important for routers, which perform QoS in software. Imagine if every router and switch in the network had to look into every packet to examine its port number. It is much more efficient if...
Configuring T38 Fax Relay for MGCP Gateways
T.38 is a standards-based type of fax relay, which treats the communication between gateways differently from Cisco fax relay. After the gateway demodulates the T.30 messages from the fax machine, it translates them into T.38 Internet Fax Protocol (IFP) packets for transmission to its peer gateway. When the other gateway receives these packets, it translates them back into T.30 signals and sends those to the fax machine. T.38 fax relay is handled differently on MGCP gateways than on H.323 and...
Providing Fax Services
Several standards govern fax transmissions. It is not necessary to know all of them to get faxes working over IP, but an understanding of the major ones helps. International Telecommunications Union Telecommunication Standardization Sector (ITU-T) standards govern such things as fax resolution, identifying tones, handshaking procedures, and transmission speeds. They have developed over time from Group 1 to Group 3 standards. The Group 3, or G3, standard is currently the most commonly used.
Securing Voice Signaling with TLS
SIP trunks use TLS to secure the call setup and teardown signaling sent over them. TLS is a protocol that provides authentication and encryption of the SIP signaling data. When configuring the SIP trunk in CallManager, you must configure a trunk security profile. Select TLS as both the Incoming and Outgoing Transport Type, and then select Encrypted as the Device Security Mode. Apply the profile to the trunk. The security negotiation and key exchange are done in the clear, so be sure to secure...
Mapping to MPLS Classes
In this situation, the company has three sites. Each site has a DS3 WAN link to the MPLS network. Notice the different routers involved. Each company site has an edge router the customer edge (CE) router. Each CE router has a DS3 link to a provider edge (PE) router. Within the provider network are multiple provider (P) routers, in addition to other devices. Suppose that a videoconference is held between users in New York and Lima. QoS on the WAN interface of each CE router ensures that the...
Classifying at Layer
A second way to identify traffic is to look at the Type of Service (ToS) field in the Layer 3 IP header. The first six bits of this field are called the differentiated services code point (DSCP) bits. They are typically set to a decimal value of 46 for voice-bearer traffic. In the past, Cisco recommended setting voice signaling traffic to DSCP 31. However, the current recommendation is to set it to Class Selector (CS)3. You can use an access list to identify traffic with a certain DSCP value,...
Configuring T38 Fax Relay for H323 and SIP Gateways
H.323 and SIP gateways use the same basic configuration for T.38 fax relay. They do not use NSE messages to signal the other gateway to switch to fax mode, unless you specifically configure it. Instead, they use H.323 or SIP messages. Configure dial peers for fax destinations, enable T.38 fax relay, and set parameters under each dial peer. If several dial peers share the same T.38 settings, you might prefer to configure them globally under the voice service voip mode instead. Dial peer...
Configuring Super G3 Fax Relay
Super G3 (SG3) fax machines negotiate the use of SG3 speed during call setup, using Call Menu and Joint Menu messages. They use the V.34 standard for modulation and the V.8 standard for signaling. V.34 is a form of pulse code modulation (PCM) that allows data transmission up to 33,600 bps. The V.8 standard describes SG3 signaling such as ANSam, Call Menu, and Joint Menu. SG3 machines can interoperate with G3 faxes. If an SG3 machine is on one end and a G3 machine is on the other, the SG3...
Securing Voice Media with Secure RTP
Media encryption and authentication using SRTP are included for MGCP gateways in the Advanced IP Services and the Advanced Enterprise Services IOS software, beginning with version 12.3(11)T1. They are included for H.323 and IP-to-IP gateways beginning in Cisco IOS version 12.4(6)T. SRTP was designed just for IP voice (not video) packets, and it was standardized in RFC 3711. SRTP encrypts the RTP payload using Advanced Encryption Standard (AES) encryption. It does not encrypt the RTP header. You...
Case Study Using a T1 Link as a Tie Line
Consider the scenario shown in Figure 8-3. This is a partial diagram of the networks at two sites New York and Boise. Both the New York and the Boise office have a PBX connected with an analog trunk line. Analog telephones are connected to the PBX at both places. The offices exchange data between them over the WAN using a T1 line. The dotted line in the diagram shows the path taken by intraoffice phone calls before the network changes were made. Figure 8-3 Using a T1 Link Between Offices Before...