Access devices should fragment large packets and provide priority queuing to critical traffic. Prioritization should be available at both the network and application level. For example, IP telnet traffic may get priority over IP SNMP traffic. Remote configuration via telnet and SNMP Management statistics. Devices should at least provide simple counters of frame rates, errored frames, congestion notifications and DE bits.
Most vendors can provide compression between their own devices.
Encryption for high security environments. In most cases, you'll be locked into a single vendor's equipment and may suffer an additional latency penalty. Automatic DLCI detection. The unit should learn DLCIs during the installation process. Routers should contain protocol-specific link optimization features such as traffic filtering and protocol spoofing.