Cisco 857W - Integrated Services Router Technical Information download pdf (Page 10)

ISR Overview and Providing Secure Administrative Access 85

ISR Enhanced Features

Although traditional Cisco routers (that is, non-ISRs) offer features similar to those

highlighted in the preceding tables, ISRs are unique in that they contain integrated

hardware components (that vary by platform) to enhance performance. For example, most

ISR models include the following enhancements:

■ Integrated VPN acceleration: By using dedicated hardware for VPN encryption,

ISRs reduce the overhead placed on a router’s processor, thereby increasing VPN

performance and scalability. Speciﬁcally, the built-in VPN acceleration hardware

supports 3DES and Advanced Encryption Standard (AES).

■ Dedicated voice hardware: IP telephony applications often use digital signal

processors (DSP) to mix multiple voice streams in a conference. They also encrypt

voice packets and convert between high-bandwidth and low-bandwidth codecs (that is,

a coder/decoder, such as G.711 and G.729, which specify how voice samples are

digitally represented in a voice packet). Voice trafﬁc uses Real-time Transport Protocol

(RTP), a Layer 4 protocol, to transport voice in a network. For increased security,

Secure RTP (SRTP) can be used, which provides AES encryption for voice. However,

because of the processor overhead required for SRTP’s encryption, dedicated DSP

hardware is required. Fortunately, ISRs can use packet voice DSP modules (PVDM) to

take over the processing of such tasks.

The Cisco 2800 series of ISRs can use PVDM2 modules with onboard voice interface

cards (VIC). Additionally, PVDM2 modules can be inserted into Cisco High-Density

Analog (HDA) network modules and the Cisco Digital Extension Module for Voice

and Fax, which can be inserted into the Cisco 2821, 2851, 3825, and 3845 ISR models.

Table 3-6 Cisco 3800 Series of ISRs

Feature Cisco 3825 Series Cisco 3845 Series

WAN technology support

ADSL and optional

G.SHDSL WICs

ADSL and optional

G.SHDSL WICs

Built-in routed/WAN Ethernet

Two 10/100/1000 Two 10/100/1000

Integrated cryptographic hardware

Yes Yes

Maximum flash memory

256 MB 256 MB

Maximum SRAM

1024 MB 1024 MB

Support for Cisco Security Device

Manager (SDM)

Yes Yes

Maximum number of VPN tunnels

2000 2500

Stateful firewall support

Yes Yes

Intrusion Prevention System (IPS)

support

Yes Yes

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