code: function CallRequest(flags, ttl, tracing, service, headers, csum, args) {
      this.type = CallRequest.TypeCode;
      this.flags = flags || 0;
      this.ttl = ttl || 0;
      this.tracing = tracing || Tracing.emptyTracing;
      this.service = service || '';
      this.headers = headers || {};
      this.csum = Checksum.objOrType(csum);
      this.args = args || [];
      this.cont = null;
  }
docs: TODO: validate transport header names? TODO: Checksum-like class for tracing flags:1 ttl:4 tracing:24 traceflags:1 service~1 nh:1 (hk~1 hv~1){nh} csumtype:1 (csum:4){0,1} (arg~2)*